In a Hybrid Automatic Repeat Request (HARQ) mode, codes transmitted by a transmitting end are not only able to detect errors, but also have a certain error correcting capability. After receiving codes, a decoder at a receiving end firstly detects errors; when the errors are within the error correcting capability of the codes, the errors are automatically corrected; when there are too many errors, which go beyond the error correcting capability of the codes, and the errors can still be detected, then the receiving end transmits a decision signal to the transmitting end via a feedback channel to ask the transmitting end to retransmit the information. In an Orthogonal Frequency Division Multiplexing (OFDM) system, Acknowledged/Non-Acknowledged (ACK/NACK) control signaling is used to indicate whether transmission is right or wrong, so as to determine whether the information needs to be retransmitted or not.
The Long Term Evolution (LTE) system is an important project of the third generation partnership organization; FIG. 1 shows a schematic diagram illustrating a basic frame structure of the LTE system in the relevant technologies; as shown in FIG. 1, the basic frame structure of the LTE system is illustrated, which includes five hierarchies, namely, radio frame, half-frame, sub-frame, slot and symbol, wherein one radio frame has a length of 10 ms and consists of two half-frames; each half-frame has a length of 5 ms and consists of five sub-frames; each sub-frame has a length of 1 ms and consists of two slots; and each slot has a length of 0.5 ms.
When the LTE system adopts a normal cyclic prefix, one slot includes seven uplink/downlink symbols each having a length of 66.7 μs, wherein the cyclic prefix of the first symbol has a length of 5.21 μs, and the cyclic prefix of the other six symbols has a length of 4.69 μs.
When the LTE system adopts an extended cyclic prefix, one slot includes six uplink/downlink symbols each having a length of 66.7 μs, wherein the cyclic prefix of each symbol has a length of 16.67 μs.
In a downlink HARQ of the LTE system, an Acknowledged/Non-Acknowledged (ACK/NACK) message is transmitted on a Physical Downlink Shared Channel (PDSCH); when a User Equipment (UE) has no Physical Uplink Shared Channel (PUSCH), the ACK/NACK message is transmitted on a Physical Uplink Control Channel (PUCCH); the LTE system defines a plurality of PUCCH formats, including PUCCH format 1/1a/1b and format 2/2a/2b, wherein the format 1 is used to transmit a Scheduling Request (SR) signal of the UE; the format 1a and the format 1b are respectively used to feed back a 1-bit ACK/NACK message and a 2-bit ACK/NACK message; the format 2 is used to transmit Channel States Information (CSI), wherein the CSI includes Channel Quality Information (CQI), Precoding Matrix Indicator (PMI) and Rank Indication (RI); the format 2a is used to transmit the CSI and a 1-bit ACK/NACK message; the format 2b is used to transmit the CSI information and a 2-bit ACK/NACK message; and the format 2a/2b is only applied to the scenario with the cyclic prefix being a normal cyclic prefix.
In the LTE system, in a Frequency Division Duplex (FDD) system, since there is a one-to-one correspondence between uplink sub-frames and downlink sub-frames, the UE needs to feed back a 1-bit ACK/NACK message when the PDSCH contains only one transmission block, and the UE needs to feed back a 2-bit ACK/NACK message when the PDSCH contains two transmission blocks; in a Time Division Duplex (TDD) system, since there is no one-to-one correspondence between uplink sub-frames and downlink sub-frames, the ACK/NACK message corresponding to a plurality of downlink sub-frames needs to be transmitted on the PUCCH channel of one uplink sub-frame, wherein a set of downlink sub-frames corresponding to uplink frames form a bundling window. The methods for transmitting the ACK/NACK message includes a bundling method and a “multiplexing with channel selection” method; wherein the basic principle of the bundling method is to perform a logic “and” operation on the ACK/NACK message of a transmission block corresponding to each downlink sub-frame and needing to be fed back in the uplink sub-frame; when a downlink sub-frame has two transmission blocks, the UE needs to feed back a 2-bit ACK/NACK message; when each sub-frame has only one transmission block, the UE needs to feed back a 1-bit ACK/NACK message; and the basic principle of the “multiplexing with channel selection” method is to indicate different feedback states of the downlink sub-frame needing to be fed back in the uplink sub-frame using different PUCCH channels and different modulation symbols on the PUCCH channel; when the downlink sub-frame has a plurality of transmission blocks, the ACK/NACK fed back by the plurality of transmission blocks of the downlink sub-frame is first subjected to a logic “and” operation (also called spatial bundling), and then is subjected to a channel selection, and finally is transmitted using the PUCCH format 1b.
In the LTE system, there are two types of uplink reference signals: one type is an uplink Demodulation Reference Signal (DM RS), and the other type is an uplink Sounding Reference Signal (SRS); wherein the DM RS is formed by a sequence on the frequency domain and the sequence is a Cyclic Shift (CS) of a reference signal sequence, different PUCCH formats correspond to different DM RS structures; the SRS is periodically transmitted, when both an ACK/NACK message and an SRS are transmitted, the ACK/NACK message is transmitted using a truncation structure, namely, the last symbol of the second slot of each sub-frame is not used to bear the ACK/NACK message; when both a CSI and an SRS are transmitted, only the CSI is transmitted.
In order to meet the requirement of the International Telecommunication Union-Advanced (ITU-Advanced), a Long Term Evolution Advanced (LTE-A) system, as the evolution standard of the LTE system, needs to support a greater system bandwidth (up to 100 MHz) and needs to be backward compatible with the existing standards of the LTE system. On the basis of the existing LTE system, the bandwidth of the LTE system can be merged to obtain a greater bandwidth, which is called a Carrier Aggregation (CA) technology. This CA technology can improve the spectrum utilization rate of an IMT-Advance system and relieve the shortage of spectrum resources, thereby optimizing the utilization of the spectrum resource.
When the LTE-A adopts the CA technology and the UE is configured with four downlink component carriers, the UE needs to feed back the ACK/NACK messages of these four downlink component carriers. In the condition of Multiple Input Multiple Output (MIMO), the UE needs to feed back the ACK/NACK message of each code; therefore, when the UE is configured with four downlink component carriers, the UE needs to feed back eight ACK/NACK messages. At present, the conclusion about the ACK/NACK message feedback is that: for a terminal of the LTE-A system, when 4 bits are supported at most for an ACK/NACK message, the “multiplexing with channel selection” method is adopted; when more than 4 bits are supported for an ACK/NACK message fed back, a method of a Discrete Fourier Transform-spread-OFDM (DFT-s-OFDM) structure is adopted; of course, other uplink control signaling also can be transmitted using the DFT-s-OFDM structure. However, at present, the LTE-A system does not provide a specific method for transmitting the uplink control signaling adopting the structure of DFT-s-OFDM, and does not indicate the location and the number of uplink reference signals in this structure.